doc/src/uml-stack-trace.html

   1 <PRE>
   2 To: Michael Richardson <mcr@sandelman.ottawa.on.ca>
   3 Cc: user-mode-linux-devel@lists.sourceforge.net
   4 From: Jeff Dike <jdike@karaya.com>
   5 Subject: [uml-devel] Re: stack trace
   6 Date: Mon, 16 Sep 2002 22:36:06 -0500
   7
   8 mcr@sandelman.ottawa.on.ca said:
   9 > Can you post (on list or web site) a "script" output of you trying to
  10 > get the right stack out of a stuck uml (tracing myself)...?
  11
  12 Yup.  Here we go...
  13
  14 Here, I attach to the tracing thread and get the stack of the current thread,
  15 which happens to be the idle thread.
  16
  17 um 1013: gdb linux 14936
  18 GNU gdb 5.0rh-5 Red Hat Linux 7.1
  19 Copyright 2001 Free Software Foundation, Inc.
  20 GDB is free software, covered by the GNU General Public License, and you are
  21 welcome to change it and/or distribute copies of it under certain conditions.
  22 Type "show copying" to see the conditions.
  23 There is absolutely no warranty for GDB.  Type "show warranty" for details.
  24 This GDB was configured as "i386-redhat-linux"...
  25 /home/jdike/linux/2.4/um/14936: No such file or directory.
  26 Attaching to program: /home/jdike/linux/2.4/um/linux, process 14936
  27 0xa014efe9 in __wait4 ()
  28
  29 # This is how you get the current task in the tracing thread - get_current()
  30 # only works in a kernel thread.
  31 (gdb) p (struct task_struct *)cpu_tasks[0].task
  32 $2 = (struct task_struct *) 0xa01c0000
  33
  34 # Get the host pid of that task.
  35 (gdb) p $2.thread.extern_pid
  36 $3 = 14939
  37
  38 # Get the current ip and sp.
  39 (gdb) shell cat /proc/14939/stat
  40 14939 (linux) T 14936 14936 883 34816 14936 64 5 3 806 7 62 12 0 0 9 0 0 2
  41 588043 142770176 5008 4294967295 2684358656 2686348640 3221223520 2686205764
  42                                                                sp ^^^^^^^^^^
  43    2685727185 73728 201392128 167776768 268444672 3222308129 0 0 17 0
  44 ip ^^^^^^^^^^
  45
  46 # the sp and ip are items 4 and 5 after the 4294967295 (on 2.2 hosts, that's
  47 2^31 - 1 rather than 2^32 - 1).
  48
  49 (gdb) p/x 2686205764
  50 $4 = 0xa01c3f44
  51 (gdb) p/x 2685727185
  52 $5 = 0xa014f1d1
  53
  54 # Where's the ip?
  55 (gdb) i sym 0xa014f1d1
  56 nanosleep + 17 in section .text
  57
  58 # look at the stack around the sp
  59 (gdb) x/32x 0xa01c3f30
  60 0xa01c3f30 :     0x00000000      0x00000000      0xa01c3f60      0xa00020a8
  61 0xa01c3f40 :     0x00000004      0xa012e891      0xa01c3f58      0xa01c3f58
  62 0xa01c3f50 :     0xa01c3f70      0xa0023667      0x00000009      0x3b023380
  63 0xa01c3f60 :     0xa01c3fa0      0xa012a21d      0x0000000a      0xa01c0000
  64 0xa01c3f70 :     0xa01c3fa0      0xa012a213      0x00000003      0x00000024
  65 0xa01c3f80 :     0xa01c3fa0      0xa0011bc4      0xa012b25c      0x00000000
  66 0xa01c3f90 :     0xa01c3fb0      0x00000000      0xa01c3ffc      0x0000000d
  67 0xa01c3fa0 :     0xa01c3fb0      0xa000c50e      0xa01812e0      0xa01c3ffc
  68
  69 # The trick here is to locate a frame near the current sp.  You're looking
  70 # for a consecutive pair of longwords (fp, ip) having the properties that:
  71 #       fp is on the current kernel stack and points further up it
  72 #       ip is a text address (if you can't recognize a UML text address by
  73 # sight, print out &_stext and &_etext)
  74 #
  75 # Starting at 0xa01c3f44, the first pair of works satisfying these requirements
  76 # is at 0xa01c3f50.
  77 # So, print that pair out as hex.
  78 (gdb) p/x *((int (*)[2])0xa01c3f50)
  79 $9 = {0xa01c3f70, 0xa0023667}
  80
  81 # Now, we start climbing the stack.
  82 (gdb) p/x *((int (*)[2])$[0])
  83 $10 = {0xa01c3fa0, 0xa012a213}
  84 (gdb)
  85 $11 = {0xa01c3fb0, 0xa000c50e}
  86 (gdb)
  87 $12 = {0xa01c3fc0, 0xa000356d}
  88 (gdb)
  89 $13 = {0xa01c3fd0, 0xa013082f}
  90 (gdb)
  91 $14 = {0xa01c3ff0, 0xa012fbdd}
  92 # Stop when you see a NULL frame pointer or gdb bitches at you.
  93 (gdb)
  94 $15 = {0x0, 0xa01513aa}
  95
  96 # Now we get the symbolic version of the stack with 'i sym' of the second item
  97 # in each pair.
  98 (gdb) i sym 0xa0023667
  99 check_pgt_cache + 23 in section .text
 100 (gdb) i sym 0xa012a213
 101 cpu_idle + 123 in section .text
 102 (gdb) i sym 0xa000c50e
 103 rest_init + 46 in section .text
 104 (gdb) i sym 0xa000356d
 105 start_kernel + 361 in section .text.init
 106 (gdb) i sym 0xa013082f
 107 start_kernel_proc + 63 in section .text
 108 (gdb) i sym 0xa012fbdd
 109 signal_tramp + 209 in section .text
 110 (gdb) i sym 0xa01513aa
 111 thread_start + 4 in section .text
 112
 113 # You can also get line number information with 'i line'.
 114 (gdb) i line *0xa012a213
 115 Line 488 of "process_kern.c" starts at address 0xa012a213 <cpu_idle+123>
 116    and ends at 0xa012a21d <cpu_idle+133>.
 117 (gdb)
 118
 119
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 129 </PRE>